In ‘Solar hot water and heat pumps’ Category

Beyond solar PV

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There’s more to renewable energy than just electricity. Renewable heat is an important alternative to gas for Australian homes and industry, writes Tim Forcey.

MANY Australians just love renewable energy. The deployment of rooftop solar photovoltaic (PV) panels continues to grow. Large wind farms are becoming more common in every state. Even the energy storage potential of the Snowy Mountains is in the news, as is Tesla with their big batteries. With these technologies and resources, we can aim to avoid the worst effects of climate change and quit burning coal and gas to generate electricity.

But there is more to renewable energy than just generating electricity. Australia also has massive opportunities for deploying technologies that harvest or create ‘renewable heat’.

It may be because Australia’s climate is not as cold as elsewhere that the term ‘renewable heat’ is rarely used here. Contrast this to Europe where, because of its key role in reducing greenhouse gas emissions, entire conferences are devoted to renewable heat. In Japan, research since the 1970s has made that country a global leader in renewable heat harvesting technologies such as heat pumps. For decades in New Zealand and Tasmania, places poorly endowed with fossil fuels, renewable heat has played an important role both in homes and more widely across their island economies.

Beyond the environmental benefits, there is a new economic reason why Australians should be interested in using renewable heat: the rapidly rising price of gas.

Three steps to all-electric

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Thinking about going all-electric, but unsure what’s involved? Here we present an overview of the steps to going all-electric and where to find more information.

IN THE past, gas was seen as a cheap and clean option for winter heating, hot water and cooking. However, the efficiency of electric appliances has improved dramatically and solar PV has fallen so much in price (and can be used to power those appliances), meaning it can now be cheaper and more environmentally sustainable to go off gas and run an all-electric home.

The ATA first looked at this in 2014 and the modelling results can be found at www.bit.ly/ATA-GVE. In summary, the results showed that even when paying grid electricity rates (i.e. without solar PV), for many Australian homes it would be cheaper over 10 years to switch from gas to efficient electric appliances, with appliances replaced as they fail or in some cases even before this. Greater savings can be found when disconnecting completely from the gas network as this eliminates the gas supply charge (costing several hundred dollars a year). The report also highlighted that new homes should not be connected to gas, as doing so would lock in higher energy costs than needed.

Savings will depend on the thermal performance of your home, the electricity price negotiated with your retailer, your gas tariffs and the efficiency of your appliances. The Grattan Institute found that a large home in Melbourne can save $1024 per year by disconnecting from the gas grid: www.bit.ly/GATCAHC

In addition, by using modern electric appliances, your home can be converted to use 100% renewable energy, whether you generate your own electricity with rooftop solar or purchase 100% GreenPower from your electricity retailer. The ATA’s latest modelling compares gas running costs to electric with solar; see p. 44 for preliminary results.

Three steps to all-electric

There are three main areas where many homes currently use gas: space heating, hot water and cooking (mainly cooktops, but ovens too). To switch to all-electric, there are now efficient options available for these uses. This article summarises the options and points to where to find more information.

Sealed with a SIP

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Last year the energy costs for this four-person household came to just $560, due to an airtight house design, a PV system well-matched to usage and a switch to all-electric. Kyle O’Farrell describes how they got there.

IN DECEMBER 2012 we were living in a small double-brick ex-Housing Commission home in the northern suburbs of Melbourne. With two growing kids sharing a bedroom and a very non-user-friendly layout, we knew it wasn’t going to work in the longer term. However, we liked where we were living and didn’t want to move. The house was built in 1953 and, aside from some minor wall cracking, it was basically sound and could probably be used as a base for a renovation. So what to do?

We asked architect Mark Sanders at Third Ecology to create three concept house designs for us: two incorporating the existing house and one a completely new build. To our surprise, the estimated cost for the new build was only around 10% more than the renovations. And, with the existing house set well back on the block, the most logical renovation design would mean building in our north-facing backyard with a significant loss of garden space, not something we were keen to do.

Thus we decided on a new build, given the benefits in orientation, block placement, reduction in project time and cost risk (renovations often throw up costly issues along the way), design layout and improved thermal performance.

The previous house was connected to the gas network, but we disconnected it during demolition and we wanted it to stay that way: for environmental, health and financial reasons, not least of which is that gas is a fossil fuel which contributes to climate change. We were also planning to install solar PV and wanted to maximise on-site usage of electricity, rather than pay the expense of a gas connection, gas plumbing and increasing gas prices. Finally, we were planning to build a very well-sealed house, so we felt that piping an asphyxiating and explosive gas into it was worth avoiding if possible. We also didn’t want the combustion products (mainly CO2 and water vapour, but also nitrogen oxides and carbon monoxide) in the house.

Around the same time, Beyond Zero Emissions released its Buildings Plan, which strongly supported going gas-free and outlined how to do it. Nice report.

Design for thermal performance

When it came to the house design, we liked the features of the Passive House approach to house construction, but knew there was a higher cost associated with the additional design, construction and certification requirements. Looking around for construction methods that could achieve similar insulation and air sealing, without additional building costs, we found structural insulated panels (SIPs). These are wall panels with a foam core and rigid panels glued to each side. The panels are weight bearing, so timber framework for the external walls is not required.

Money-saving results in Melbourne

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This family of four saved around $250 last winter by heating their home with a reverse-cycle unit instead of their older gas ducted system. They went on to swap out the remaining gas appliances, disconnect gas from their property and save even more. Stephen Zuluaga explains.

IN 2012, our family moved to a three-bedroom brick veneer townhouse in the south-eastern suburbs of Melbourne. The house was constructed in 2001 and it’s likely that’s when its original gas ducted heating, water heater and stove were installed.

We’d always been interested in keeping our energy costs down, but, like many people, we just assumed that high gas bills in winter were a part of life. We found that our two-month gas bill spiked significantly in winter due to heating, rising from around $80 in summer up to around $400 in winter.

Then in September 2015 I came across an article on The Conversation which proved to be a turning point. Tim Forcey’s article1 described research undertaken at the Melbourne Energy Institute which suggested that efficient electric appliances—heat pumps—could heat your home more cheaply than gas.

Intrigued, I got in contact with Tim to learn more. He introduced me to the My Efficient Electric Home Facebook group and, through contacts made there, I spoke to many efficiency experts and interested householders like myself about ways to reduce costs and increase efficiency.

In hindsight I can see that I was heading down the path of all-electric, but I wasn’t really looking at it like that at the time: it was just about replacing inefficient appliances with efficient ones.

There are many motives for wanting to improve efficiency and for us the primary driver was financial. Over the course of converting our house to all-electric, I spoke to others who had a combination of environmental, efficiency, financial and technological motives. I really like the fact that no matter what your motive is, you can get an outcome that both lowers costs and reduces environmental impact.

Efficient hot water buyers guide

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If your old hot water system has seen better days, maybe it’s time for an efficient replacement. We show you how solar and heat pump hot water systems work, what’s available and how to choose one to best suit your needs.

ONE of the biggest energy users in any home is water heating—it can account for around 21% of total energy use (on average, according to YourHome), at a considerable financial cost each year. Water-efficient appliances are one way you can reduce energy use—for example, you could replace an inefficient showerhead (e.g. some use 20 litres per minute) with the most efficient, which uses less than 5 litres per minute, saving water and water heating energy each time you shower. But far greater energy reductions are possible if you replace a conventional water heater with a heat pump, solar thermal or solar electric system.

Such systems have the added advantage of reducing your greenhouse gas emissions. For example, for an average family the reduction can be as much as four tonnes of CO2 per year—the equivalent of taking a car off the road!

What we do and don’t cover

From an efficiency and environmental point of view the future of household energy is electric. The rise of rooftop solar and the availability of GreenPower means that households can use 100% renewable energy to run their appliances, including hot water systems.

This means we don’t cover efficient gas hot water options such as gas instantaneous in this guide, although the solar thermal hot water systems listed do have gas boost options. Gas used to be seen as the cleaner energy choice, at least when compared with burning coal, but there are better non-gas appliances available to households now. And changes in the gas market mean gas prices are on the rise. Replacing a hot water system with a modern solar thermal or electric one is often the first step in disconnecting from the gas grid, and the associated costs and greenhouse gas emissions.

We cover systems designed for household hot water that can run from renewable energy, including electricity, and ambient and solar thermal heat. These include heat pump, solar thermal, electric instantaneous and the newer kids on the block, PV diversion and direct PV water heating systems. Heat pump systems can be designed for other purposes in the home such as pool heating or hydronic heating, but these are out of the scope of this guide.

Getting into hot water

Five reader stories and five different systems that illustrate there’s more than one way to get into hot water!

Jen Gow has tried out both flat plate and evacuated tube solar hot water systems, and discusses the differences.

Don’t dismiss resistive element hot water

For Dave Southgate, converting to an all-electric house did not involve using a heat pump for hot water. Here’s what he did instead.

How to save money with a hot water heat pump

Jonathan Prendergast shares his quest to reduce his hot water bills by switching to a heat pump.

Troubleshooting issues with solar hot water

Ewan Regazzo’s electrical engineering background was put to good use troubleshooting a faulty solar hot water installation. It’s now working well, but there were several issues along the way.

Resistive versus gas

Linda and Mike Dahm were surprised when the energy costs for their dual occupancy homes, one with solar PV and an electric resistive hot water and one with gas hot water, worked out about the same. Here’s what happened.

Questions for hot water system suppliers

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It’s best to sound out an installer to check their reliability before handing over your hard-earned cash. Have they successfully installed this particular hot water system before? What happens if they go out of business? Here are some key questions to get you started.

Questions for heat pump installers
It’s important to differentiate between high quality heat pumps and those that are less efficient. The best heat pumps will have a coefficient of performance of 3.5 to 4 or higher, while some of the lesser quality heat pumps may be down at 2 to 2.5. Some tradespeople will also tell you that heat pumps don’t work in cold weather. A more accurate statement is that some brands don’t work in the cold, while others actually work quite well. One way to compare heat pumps is by the number of STCs they receive for your climate zone, available at www.bit.ly/HW_STCs, with more STCs meaning they operate more efficiently in that climate zone. “They’re too noisy” is also another comment about heat pumps, whereas only some brands are actually noisy – look for a heat pump with a noise rating less than 50dba. Here are some questions to help pick a quality heat pump.

What’s the heat pump’s coefficient of performance?

What is the heat pump’s coldest operating conditions, or operating temperature range?

What is the heat pump’s noise rating?

Does the compressor have a block out timer/timing function?

Does the heat pump have a resistive element? (If so, it could mean that the actual heat pump doesn’t work as well as others. You’d also need to be wary of what impact the resistive element could have on household electricity use.)

What is the tank warranty, compressor warranty and installation/workmanship warranty?

What’s the process to enact a tank or compressor warranty after the installation warranty has expired?

Are there any additional costs such as safety switch costs, set up for block out timing (to match solar PV generation times), or extra cost for an elevated work platform?

Questions for solar thermal installers
Solar thermal systems can take a number of days to install due to the plumbing and roofwork involved. Quiz your installer about the full installation process.

How well does the system perform in overcast conditions?

Will my roof need to be strengthened for a close-coupled system?

What is the tank, collector, booster and installation warranty?

Will my system need a tilt frame?

Does the system come with freeze protection?

How long will it take to install the complete system?

Island of energy: community-owned and renewable

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Denmark’s Samso Island went from complete reliance on imported oil and coal to 100% renewable electricity in just a decade. Jayitri Smiles and Nicky Ison explore the community and government partnerships that made it happen.

DURING the global oil crisis in 1973, Denmark began to think creatively about how to supply cheap energy to their population. As they built their first wind turbine, they were unknowingly establishing themselves as future world leaders in renewable energy.

Today, Denmark aims to have renewable energy powering 100% of their country by 2050 and to eliminate coal usage by 2030. These targets build on a track record of success: since the 1990s Denmark has witnessed the quadrupling of renewable energy consumption.

The creation of the world’s first fully renewable energy powered island, Samso, is an exemplar of Denmark’s leadership. Not only has Samso become a carbon-negative region, but it has accomplished this world-first using community investment.

In 1997, Denmark’s Minister for Environment Svend Auken was inspired at the Kyoto climate talks. He returned home with a passion to harness the collective efforts of local Danish communities in a way that promoted self-sufficiency in renewable energy. Auken held a competition, which encouraged Danish islands to consider how their clean energy potential could be achieved with government funding and matching local investment.

The most compelling application came from Samso, a small island west of Copenhagen with a population of 4100. This island of 22 villages, at the time run purely on imported oil and coal, was suddenly thrust into the global spotlight and, through a combination of local tenacity, investment and government funding, transitioned to 100% renewable power in just a decade.

At the heart of this energy revolution sit Samso’s community-owned wind turbines. Onshore turbines with a generation capacity of 11 MW offset 100% of the island’s electricity consumption. Another 23 MW of generation capacity from ten offshore turbines offsets Samso’s transport emissions. Most (75%) of the houses on the island use straw-burning boilers via district heating systems to heat water and homes, and the remainder use heat pumps and solar hot water systems.

The extraordinary result is a carbon-negative island and community. The island now has a carbon footprint of negative 12 tonnes per person per year, a reduction of 140% since the 1990s (compare this to Australia’s footprint of 16.3 tonnes per person in 2013 and Denmark’s overall footprint of 6.8). Not only is the island energy self-sufficient, they now export renewable energy to other regions of Denmark, which provides US $8 million in annual revenue to local investors.

And Samso is not slowing down. Highly motivated, knowledgeable and passionate locals are aiming for the island to be completely fossil-fuel free by 2030. They plan to convert their ferry to biogas and, despite already offsetting their vehicle emissions via renewable energy generation, residents of Samso now own the highest number of electric cars per capita in Denmark.

Farming Renewably: Reaping the benefits

I’ve read many inspiring articles in ReNew from individuals trying to live more sustainably and lessen their impact on the planet. This article takes a slightly different approach–a rural perspective–to demonstrate that it can be commercially viable to run a farming enterprise using systems that are truly renewable, whether that’s for water, electricity, housing, food, livestock, pasture or wildlife.

Our journey to sustainable farming began in 1993, when my wife Roberta and I purchased a 60-acre property in the south-west of WA with the twin objectives of restoring the degraded land and becoming as self-reliant as possible. The land included pasture that was totally lifeless and neglected, along with a dam, two winter streams, old gravel pits and two areas of magnificent remnant native forest. We wanted to be independent for water, electricity and as much of our food as was practical. Withe fewer bills to pay, we could work fewer hours off the farm–which was very appealing.

As a registered nurse with no farming experience, I was on a vertical learnign curve. Luckily, Roberta has a dairy farming background and, with her accounting experience, is a wizard at making a dollar go a long way.

When we began, we were both working full-time. We spent the first two years establishing a gravity-fed water supply, preparing the hosue and shed sites, and fencing the property, including to protect remnant bush from planned livestock. We also planted over a thousand native trees and shrubs, plus a few ‘feral’ trees for their air conditioning and fire-retardant properties.

Efficient hot water buyers guide

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If your old hot water system has seen better days, maybe it’s time for an efficient replacement. We show you how solar and heat pump hot water systems work, what’s available and how to choose one to best suit your needs.

As the price of energy keeps escalating, the idea of being able to reduce energy use has never been more attractive. One of the biggest energy users in any home is water heating—it can account for around 21% of total energy use (on average, according to YourHome). Water-efficient appliances are one way you can reduce energy use, but far greater energy reductions are possible if you replace a conventional water heater with a solar or heat pump system.

Such systems have the added advantage of also reducing your greenhouse emissions. For example, for an average family the reduction can be as much as four tonnes of CO2 per year— the equivalent of taking a car off the road!

Currently only SA and Victoria offer state government rebates for solar and heat pump water heaters, but STCs (small-scale technology certificates; each STC is equivalent to the one megawatt hour of electricity the system will displace over a 10-year period) are still available across Australia.

STCs can save you a great deal on the cost of a new water heater, making it more economically viable. Note that the rebates and STCs are usually arranged by the supplier so you don’t need to do any paperwork to receive the discount. The price will probably still be higher than a similarly sized conventional water heater but the savings made in running costs will pay for this difference in 5 to 10 years in most cases.

How they work

SOLAR HOT WATER SYSTEMS

A solar hot water system usually consists of a hot water storage tank connected via pipework to solar collector panels. These collector panels are placed on a (preferably) north-facing roof. The tank can be situated immediately above the panels on the roof (a close-coupled system), above and a small distance away from the panels within the roof cavity, or at ground level (a split or remote-coupled system). For split systems, a pump and controller are required to circulate water through the panels. The collectors are usually mounted at an angle of no less than 15° from the horizontal (the minimum angle for close coupled systems to ensure correct thermosyphon operation), although often a lot steeper to optimise the system performance for winter.

As the sun shines on a collector panel, the water in the pipes inside the collectors becomes hot. This heated water is circulated up the collector and out through a pipe to the storage tank. Cooler water from the bottom of the tank is then returned to the bottom of the collector, replacing the warmer water.

Some systems don’t heat the water directly but instead heat a fluid similar to antifreeze used in vehicle cooling systems. This fluid flows in a closed loop and transfers the collected heat to the water in the tank via a heat exchanger.

HEAT PUMPS

A heat pump is a process used in refrigeration where heat is moved, or ‘pumped’, from one medium into another. Air conditioners and refrigerators are the most common forms of heat pumps. For example, in a refrigerator, heat is pumped from the food and dumped to the air outside the fridge via the coil at the back.

Heat pump hot water systems are electric water heaters that concentrate low-grade heat from the air and dump it into the water storage tank. They are much more efficient than conventional resistive electric water heaters: compared to resistive heaters, they are generally capable of reducing year-round energy requirements for hot water by at least 50%, and by as much as 78% depending on the climate, brand and model.

The most common systems are air-source heat pumps, but ground-source heat pumps are also available. While their efficiency can be even higher than an air-source heat pump, they are a great deal more expensive and are often not economically viable. But if efficiency is the primary goal then they should be considered, especially if you are in the market for both water and space heating systems. We looked at ground-source heat pumps in ReNew 112.

Cool-climate build

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Designing a house to be as energy efficient as possible is one thing; actually achieving this can be another task altogether. Meg Warren and Fraser Rowe describe their building challenges and eventual rewards.

OUR quest to build a new sustainable home began about four years ago when we purchased vacant land in cool-climate Beechworth in north-east Victoria. We wanted a sizeable block, big enough for rainwater tanks and a small edible garden, but also walking distance from shops, cafes and work. But our most important criterion was solar access. We found just such a block with the added bonus of a well-grown oak to the west, offering summer shade. The real estate agent seemed not to notice these attributes: to them the block was just a problem to sell due to its odd shape and no services.

Shifting from a rural property of 18 acres to an urban block of less than 1000 m2 brought a number of challenges. Our design was limited by council regulations, fences and boundaries, as well as a high, dense hedge on our neighbour’s property to the east.

Design phase

To help us achieve a truly energy-efficient design we engaged building designer Tracey Toohey whom we’d worked with on our previous owner-built rammed-earth house.

Tracey asked us to rate three areas to indicate our level of commitment to sustainability in the build. The first rated our desire for energy efficiency against overall cost. The second, and more difficult for us, assessed the compromise between sustainable materials and efficiency, and the third, between sustainable materials and cost. This interesting exercise helped us clarify our goals.

We worked intensively with Tracey for months, honing the design. Thought went into the glazing type and size to balance it with the floor area, together with the placement, type and amount of internal thermal mass, creation of airlocks, height of ceilings and all the other dimensions that impact on the energy rating. We also allowed for wider than usual walls to fit in more insulating layers beyond the standard 90 mm bulk insulation. Attention was given to the need for summer shading, rainwater harvesting and greywater recycling.

Low-cost solar heating

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Solar hydronic systems don’t have to be complex and expensive. Chris Hooley describes his simple and low-cost solar hydronic heater.

WINTERS in Melbourne used to be predictable: four months of sog from May to September. However, whether due to climate change, El Niño or simple drought, the winter of 2010 had a particular impact on me in that I kept coming home in the late afternoon to a very cold house, lit by shafts of brilliant winter sunshine. “Wouldn’t it be good,” I thought to myself, “if I could catch some of that energy and keep the house warm?”

I had a rough idea of what was available to make water hot using sunlight. Being a devoted handyman and incurable tinkerer, the seed of an idea took root and grew. My basic parameters were simple: I wanted a completely off-grid, stand-alone system that would ‘catch’ some energy in cooler months and put it to good use, without having to be plugged in or modified seasonally. Since the house already had gas central heating, the system would not need to meet all heating requirements but would rather take the edge off the cold on days when the sun happened to shine.

With this in mind I prowled eBay and mentally drew up plans until I could stand it no more and started buying parts. The key elements consisted of an evacuated-tube array piped to a fan-forced radiator. The collector heats the water and a pump transfers the hot water to the radiator in the house. A fan forces air through the radiator and into the room, heating it.

The system would be controlled by a thermo-switch and powered by a pair of 20 W PV panels. To avoid it freezing solid overnight or boiling away in summer and to eliminate the need for seasonal draining and refilling, I resolved to fill the whole system with car radiator coolant.

Know your renewables – Solar hot water system basics

Solar water heaters have been around in their modern form for almost 100 years. However, there is a lot of confusion between solar water heaters and solar photovoltaics, the common ‘solar panels’ that generate electricity directly.

Solar hot water (SHW) systems are what’s known as a solar thermal technology. They use the sun’s heat to heat water, either directly or indirectly. There is generally no electricity involved, except for the use of circulation pumps and backup boosting in some systems.

The basic design is that a flat panel that contains tubes for the water to flow through is connected to a storage tank. Water flows from the tank, is heated in the panel by the heat of the sun and flows back to the tank as heated water. However, there are a number of different configurations of tank and panels, and each has a different method of getting the water to the panels and back to the tank.

The simplest type is the close-coupled direct heating system. In this, the solar collector is mounted on the house roof with the water tank mounted directly above it. Water flows from the tank into the collector where it is heated by the sun. As warm water is less dense than cold water, the warm water rises up through the collector tubes and flows back to the tank as heated water, drawing colder water from the tank into the bottom of the collector for heating. This system is called thermosiphoning and is the most reliable and simple of the solar thermal water heating systems.

The other common system usually has the tank mounted at ground level, either inside or outside the house. A pump circulates water from the tank up to the collector, where it is heated and then flows back to the tank. A pump is needed in such systems as thermosiphoning only works when the tank is mounted above the panels. The pump is controlled by a special controller that has multiple temperature sensors in the tank and the collector.

This type of system is known as a remote-coupled or split system. It is more complex than a close-coupled system due to the added complexity of the pump and controller.

Panel types

While there are two main types of systems, there are also two main types of solar collectors. The first is the flat-plate collector, which is a flat, insulated box containing an array of pipes connected to a metal sheet, all painted black. The metal sheet absorbs incoming solar heat and transfers it to the attached pipes and hence the water inside them.

Monitoring a rooftop solar hot water system

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David Gobbett is using a Netduino microcontroller to monitor the temperature fluctuations in his rooftop solar hot water system.

For decades, the first or only solar appliance installed by many Australian households was a rooftop solar hot water system. My parents installed one on our family home in Adelaide in the mid 1970s. In my current home we installed a conventional 300-litre rooftop system in 2006. Superficially at least, the design seemed to have changed little over the intervening years. In both cases an electric booster was connected to off-peak power, which is switched on automatically by the power meter from midnight to 7 am each day.

To reduce our energy consumption over summer, we turn off the electric booster at the main switch during late November to late March, and we still have adequate hot water most of the time. However, occasionally we unexpectedly get caught short of hot water, and at those times it’s been frustrating having no way of knowing how hot the water in the tank actually is.

Another concern with switching off the booster is that there are potential health issues when hot water system temperatures are allowed to drop below 60 °C. Lévesque et al. (2004) indicate that Legionella bacteria can grow in water temperatures up to 45 °C, but that growth stops above 55 °C, and over 60 °C the bacteria are killed. Even in hot water systems with the thermostat set to 60 °C, the lower part of the tank can remain at temperatures that are optimal for Legionella growth. It would be nice to avoid this—but that would entail having a way to sense the temperatures in the tank, which is high up on the house roof.

A project idea was sparked when a friend showed me that he was using a small microprocessor board to log solar PV power outputs. He had also connected a sensor on his water meter so he could log household water consumption. This inspired me to start on my own project to get a better understanding of what the temperatures in my solar hot water system were doing.

My interests in this project were to:
• minimise unnecessary power usage
• know when we’re running low on solar hot water, so the booster can be turned on
• minimise any risk associated with Legionella.

Setting up the temperature logging

Although I have experience as a computer programmer, I had never programmed microprocessors or worked with such things as temperature sensors. After some internet research I decided to use 1-wire devices (1-wire is a technology by which sensors and other devices can communicate). I took the plunge and purchased:
• 1-wire temperature sensors (DS18S20; 10 of these cost $18). These sensors operate over a temperature range of -55 °C to +125 °C. Several of these sensors can be connected to a single cable to form a mini network where each sensor has its own unique identification.
• a USB to 1-wire adaptor, to allow me to connect the sensors to my PC for testing (DS9490R; $28)
• a Netduino Plus microcontroller (US$70) which included a network socket and micro SD memory card slot. (See side box ‘Arduino style microcontroller boards’).

I proceeded to build the system in small steps. First I soldered three of the 1-wire sensors to a length of old telephone extension cable and then used the 1-wire to USB adaptor to connect them to my PC. Using free software (from www.maximintegrated.com) I was reassured that I had wired them correctly (phew!). Then with some extra lengths of phone extension leads, I inserted the sensors under the insulation at one end of my hot water tank and immediately saw big differences between the top, middle and bottom of the tank, as well as temperature changes in response to hot water use in the house. This was encouraging since it showed that I could get useful temperature readings from the outside of the tank.

Reducing emissions with a boatie’s lifestyle

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Living on a boat instead of the great Aussie dream of a 40-square house can greatly reduce your environmental footprint. Geoffrey Chia explains how he plans to do that in the future with his newly acquired catamaran.

IT IS feasible to drastically reduce personal fossil fuel consumption, carbon emissions, fresh water consumption and waste production without significantly compromising quality of life. Many yachties are already living proof of this fact. I plan to demonstrate and live this myself, on my newly acquired Mahe 36 catamaran, using the latest devices available to show that modern appliances and electronic technologies can be part of a sustainable life. The technology is sufficiently mature and I have sufficient equity to embark on this project now.

I am unable to address issues of embodied energy, which can only be addressed by the manufacturers of items and materials. I will only be purchasing products which are commercially available. Nevertheless, as the embodied energy of standard houses and appliances is much greater than that of the items and materials used in this project, the net benefits, taking into account both embodied energy and long-term daily consumption and waste, will be far superior in this project, compared with our standard lifestyle.

I will not be able to completely eliminate fossil fuel use, but intend to show we can drastically reduce our carbon footprint by a tremendous amount, hopefully by at least 80% to 90%, fairly easily.

This project will be a proof-of-concept, low-footprint residential project in the first instance. I will continue to work, with my car parked near the river for workday commuting. Coastal and ocean passages are options for the future when I have reduced the substantial loan that funds this project.

Modern appliances
The most important aspect here will be the utilisation of energy-efficient and energy-saving electrical devices. Air conditioners, fridges, freezers and plasma TVs are the major consumers of electricity in Australian households, while heaters can be a major electricity guzzler in colder climates.

Incandescent lights are also terribly wasteful, converting less than 10% of electricity to light, the rest being wasted as heat. Hence all lighting will be LED lights, which are now more efficient than even compact fluorescent lights. LED lights contain no mercury and have a projected lifespan of 30,000 to 100,000 hours.

From the archive: Use the sun to heat the house

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In ReNew 116 we look at a variety of hydronic-based heating systems. In this article from ReNew 95, Michael Harris gives a good overview of hydronic space heating systems that use evacuated tube collectors for solar boosting. We hope it gives good background to the hydronic heating feature in ReNew 116.

The idea of using the sun to provide heating for your house is very attractive. In the southern states of Australia space heating is the biggest energy user and in country properties heating can be very expensive if you are using bottled gas and hard work if you are using firewood. Solar energy is free, and produces no greenhouse gases. It could be a great solution.

The increasing use of hydronic heating has the potential to make solar heating easier. Hydronic heating systems distribute heat through a house by running hot water through pipes to radiators in each room or to coils in the concrete slab. It is easy to shut down the radiators or coils that you do not need and the system can be quite efficient. The water can be heated by a gas or wood-fired boiler or by solar.

So the solution to your heating needs sounds simple. Put in a hydronic heating system and bung some extra solar panels on the roof. Whoopee, we have solar heating. However, unfortunately it is not that easy.

For many years solar water heating in Australia has been done by using flat plate collectors. These collectors are basically an insulated box with a glass top and a sheet of metal with pipes attached inside the box. The sun shines, the inside of the box gets hot, the sheet of metal gets hot and the pipes containing the water get hot. It works well when it is sunny.

However it does not work so well in cloudy conditions. And when it is winter and it’s cold, when you need the system to perform at its best, these collectors provide very little energy input. Although the flat plate collectors would give you some benefit, the cost of the extra collectors far outweighs the benefits.

So what has changed?

Affordable evacuated tube-based collectors have come onto the Australian market. These work differently to flat plate collectors and are much more efficient in cold and cloudy conditions. The tubes have a double glass wall like a thermos flask. In between the two walls is a vacuum which is an excellent insulator and minimises heat loss. On the outer wall of the inside tube is a selective surface which maximises the absorption of solar radiation. When faced north the curved outer surface of the tubes will effectively collect heat from the sun at all times of the day because reflection off the glass surface is minimised.

So you end up with a number of benefits; a selective surface that absorbs more heat, a vacuum that stops that heat escaping and a round surface that reduces reflection hence collecting more heat. The result is a solar panel that collects more heat, especially in winter.

How it works

At the time of writing, one green plumber had been installing systems using the Sunplus CPC Solar brand of evacuated tubes. The typical system consists of eight 12 tube panels, a 1200 litre stainless steel tank with two heat exchange coils, a controller and solar circulator pump, mixing valves, expansion tank, a combination boiler to back up the system, and the components for the hydronic system (pipes, pump, valves and radiators or floor coils). A system of this size would be capable of heating a 25 square house.

When operating, the sun heats the water in the pipes in the evacuated tubes. A sensor detects when the water reaches the appropriate temperature and switches on the circulation pump. The pump circulates hot water to the heat exchange coil in the bottom of the storage tank. As the water heats up it expands and pressure in the circuit builds up. Rather than vent the pressurised hot water (which would waste water) the pressure is taken up by the expansion tank.

A coil in the top of the tank heats up with the water in the tank. When the pump for the hydronic heating system is turned on, heat is transferred to the water circulating around the hydronic heating circuit. If the solar system does not heat the water in the hydronic loop adequately, the boiler comes on and boosts the temperature. Domestic hot water for general household use can be heated by a separate heat exchange coil in the tank.
A critical aspect of the system is the mixing valves. The evacuated tubes are capable of generating high temperatures. Reliably regulating these temperatures is essential for both safety and reliability reasons. Boiling water can burn someone who touches a radiator, crack a concrete slab with embedded heating coils, or kill the boiler that boosts your system.

What does it cost?

Hydronic heating systems are not cheap. As a rule of thumb, the cost per radiator (including piping) is about $1000. The alternative, an in-slab floor coil, can be around $4500.

The solar components to heat a 25 square house would work out something like this; evacuated tubes $9000, custom-built tank with coils $4500, and combination boiler $2500. Installation and miscellaneous hardware add about $2500. So you can be looking at total costs for the hydronic heating of between $6000 and $10,000, and the solar heating system could be close to $19,000.

Some government rebates also apply to these systems. The solar heating system above would receive a $1500 rebate in Victoria, bringing the cost down to around $17,500.

Although this is quite a lot, remember that these systems also supply domestic hot water. A solar water heater typically costs around $5000 so the actual additional cost for the solar boosting of the heating system may only be around $12,500.

Savings

So is it worth it? To answer that, you need to take into account the life of the system. The chief cost components—the evacuated tubes, tank and piping—should have a very long life, 20 to 30 years would not be unreasonable. The pumps and valves may need replacing during that time but they are a relatively small part of the cost.

Running a hydronic heating system such as this would be likely to cost around $600 per annum in the city or about $1700 per annum in the country using bottled gas. This means the heating costs over 20 years in the city would be $12,000. In the country it would $34,000.

If the solar boosting provided half of the hot water needs then it would save $8000 in the city and $22,644 in the country. The savings are even greater when you add the domestic hot water savings and take into account the likely increases in energy costs over the next 20 years.

Performance

These systems are new in Australia so there has not been enough time to see if they will deliver what they suggest. But the results look promising. Lets look at the experience of some people who have put these systems into their homes.

Gordon, from Arthur’s Creek in Victoria, has installed a system with 15 panels of six tubes each, connected to a 1100 litre storage tank. Last winter his gas boiler was consuming two bottles of gas every five days, at a cost of $160! ‘When we realised how much it was costing us to run our heating we stopped using it. We only turned on the heating when we were desperate.’

Gordon’s new system was installed last spring so it has not yet had the chance to run through a winter. But based on how it’s been performing it looks promising. ‘The system started to operate in spring when the daily top temperature was typically 18 to 20 degrees. On the first day the tank temperature went from 15 to 45 degrees and within a few days was over 80 degrees and went off scale on the temperature gauge. Ever since it has been boiling and sitting at close to 100 degrees Celcius.’

Mitch from Seymour has put in a system to assist the heating of his 65 square house. He was first inspired by an item in ReNew on evacuated tubes. Later he was staying in South Georgia (near the Falkland Islands) and was astonished to see the very same evacuated tubes on the British Antarctic Service buildings. South Georgia is close to the Antarctic and experiences very low temperatures and strong cold winds. Mitch reasoned that if these evacuated tubes worked there, they would certainly work in central Victoria. His system uses 18 six-tube panels, storage tanks with a capacity of 1,400 litres and a combination of floor coils and radiators to heat the house.

Glen from Greendale installed a small system with six panels with six tubes each, and an 880 litre tank. Glen wanted to test his system performance so he installed sensors in the tank and panels. The system was installed in September and was providing plenty of hot water for domestic use, (the hydronic system was not being used because it was summer).

During Christmas Glen went away on holiday. When he came back the system was not working. He checked and found the sensor in the tank had melted and popped out of the tank and the collector sensor had not only failed but the heat shrink on it had melted off. He has since killed several more sensors while playing around to see what temperatures he could get from the system.

While the thermal performance of evacuated tubes in cold conditions and low light conditions suggests that these collectors may make solar hydronic heating a viable option, we will need to see how these systems perform through a full winter. It is not hard to get hot water in summer—winter is the real test.

It is also important to remember hydronic heating systems need to be installed by an experienced professional and adding a solar component increases the complexity of the system. Readers thinking about trying this kind of system should be cautious and do their homework.

Farmhouse solar hydronics

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In issue 116 we visit Ian Hill’s 1970s home which has been retrofitted with solar-powered water and household heating. Here’s is a detailed version of that article, with more of the nitty gritty on system design for those about to embark on such a project.

Nearly nine years ago we made a tree change to active, semi-retirement. We bought a farm in West Gippsland, left behind seaside Frankston, and went niche beef farming for a change in lifestyle. We’re happy to say it was a good decision.

The farm came with a large home—16 rooms over five levels with two open-plan living and entertaining areas—the main selling point being we liked this style years ago.

The three concrete slabs stepping down the rolling red soil hills already had hydronic in-slab tubing, heated from a diesel furnace along with the tap water. Cooking was done by bottled gas, and there were three slow-combustion wood heaters in the two living areas.

Philosophy and design

We are very keen on sustainability and want to minimise our carbon footprint, both in the home and our farm’s beef production. We were prepared to spend some money converting the heating system for a large reduction in running costs and emissions. The farm has many large trees and limbs are always falling, so using solar-powered heating and hot water, boosted by a wood-fired heater, seemed like a sensible idea.

We found the solar collectors we wanted and set system parameters. Our plumber designed and built the conversion, changed the skylights, re-flashed the house and updated much of the water collection. We added ideas as it was built over several months.

The home

The climate is cool temperate with few frosts and the house is sited on a southern slope in foothills.

We are at latitude 38.005°. There is some unavoidable morning shading in winter from a roadside glider possum habitat of magnificent eucalypt trees over 40 meters high, 30 meters away and uphill on the northern road boundary. The outside temperature ranges between 2°C and 42°C but the house has such a large thermal time constant that living areas stay between 17°C and 22°C in winter, and no more than 25°C after a run of hot days.

The house design is classic 1970s double brick with rough-sawn, exposed beams in eight meter cathedral ceilings.It had hardwood french and other windows with single-glazing throughout, and sad plastic-vented skylights. Everything was coloured mission brown.

The designer ignored the 16 kilometre view to the Strzelecki Ranges and the valley below, and modern principles of house alignment for passive heating and cooling. However, at least the sun does not load up the interior. There are a few, small windows to the east, with excellent shading from canvas blinds, and large french windows to the west. These are shaded by a pergola and close battens. The home’s north face is stepped into the hill and the windows are totally shaded by a brick cloister with archways: a very sensible design providing a great spring breakfast area.

The kitchen, living and lounge rooms, study and billiards rooms are open plan and interconnected on three levels, which does create air currents, especially with such high ceilings. We have been slowly renovating, as one does with a retirement income.

The aim is to convert major glass in living areas to high-efficiency glass and to install as much double glazing as we can afford. So far our plumber has retrofitted seven double-glazed, openable skylights. The local glazier replaced 11 clearstory windows and made three panels openable to draw up cooling air from the lower levels when a summer cool change arrives.

We use pressurised tank water for most of the home, buildings and farm animals. There are 245,000 litres available in concrete tanks, linked by a 50mm buried ring main. Our local irrigation contractor built a fire sprinkler system for all buildings on the farm, which was essential when the wind changed during the Black Saturday bushfires in 2009. Our 100-year average rainfall is 1100mm; we received 1178mm in 2010 so we always have an excess of stored water.

There is a 1.5kW solar power system on the roof, bringing an income and well offsetting the minor energy drain from the small pumps moving water into the hydronic heating and up to the solar collectors.

The service courtyard where most of this hybrid heating and hot water system is hidden looks Heath Robinson, but it is a credit to our local green-accredited plumber at Baw Baw Plumbing and his team. He always knows about the latest efficiency innovations and was a terrific speaker at our Landcare group’s Green Energy field day.

Heat storage

A custom made 1000 litre stainless steel tank with 75mm of insulation and a small header tank is the heat storage. It’s similar to those made for the local dairy industry. Hot water is not drawn from this water but via three heat exchanger coils in the tank, with the solar one at the base, the hydronics one at the centre and the hot water service at the top. Each is 11 metres long.

From sellers’ claims, the most efficient collectors I could find were Ritter (labelled APR), a Chinese-made German design imported by Sunplus CPC. We bought 1.6m long evacuated tubes in banks of six, with parabolic mirrors to direct extra sunlight under the tubes. Our budget limited us to triple the normal number of tubes recommended for hot tap water and a 1000 litre hot water storage tank.

The collector bank of 36 tubes is fixed to a 1.6m by 4.4m aluminium frame facing 15° west of north. I asked for it to be tilted steeper than the roof’s 17° at a calculated winter solstice angle of 60° to collect maximum energy for winter. This reduces excess summer yield and steam problems.

Importantly, the plumbing route for the tubes allows us to add more down the track.

The north roof with evacuated tube collectors for the heating system and a 1.5kW solar power system.

Inside the solar control and storage area

Solar-heated water pumping

This is a rainwater-filled closed loop heat-exchanger. Water from the storage tank coil is lifted about five metres up to the solar array by a 3-speed 30 watt 240v hot water pump with throttling valve, giving infinitely variable flow. It usually runs at 0.2 bar boost. A Zilmet model 20013 50 litre cylinder stores system over-pressure up to four bar from summer days, backed up by a blow-off valve to save water loss on hot days.

Relief valves

Four high spots in the solar array and wood heater circuits have auto air-bleed valves, allowing only air and steam to escape.

Wood-fired slow combustion heater

We changed the third wood heater to a gas unit for quick response to a cold home.

After the first winter with the new system, an existing free-standing Saxon unit in the living room was retrofitted with a 550mm tall stainless steel heat exchanger in the first part of the flue. It burns quietly from late autumn to early spring on wind-fallen mountain ash and blackwood harvested around the farm. Water to the flue exchanger is drawn from the base of the storage tank and delivered back to the top. Piping is about 25 metres long and rises about 3 metres. It is insulated with 25mm thick foam tubing and cased in colorbond. A 240v thermostat in the output pipe in a wall behind the heater senses output temperature and controls another small circulating pump at the storage tank, moving two litre slugs of hot water at 50 °C into the storage tank every few minutes. This heater provides around half our total hydronic heating in winter.

Gas boilers

Tap water is delivered via an instantaneous Rinnai V1500 gas boiler which adds heat if stored water is not 50°C. There are no adjustments for the home owner. Electronics in this unit can be damaged by our emergency home generator, so we cannot run the hot water when mains power fails, which it does for several hours at least four times per year.

Hydronic water supply is delivered to the mixing valve via a Sime Format 34e instantaneous gas boiler, rated at 11.2kW to 34kW, large enough to heat the whole home on its own. It adds heat if needed and has user-adjustments for output temp (set to 35°C). Its instruments display output temperature and pressure. The pump within this unit is also triggered by the thermostat in the master bathroom, sending heated water to a Hydrotherm P-600 Platinum tower rail, 2.2m by 600mm wide, helping provide some extra hydronic heating to the bathroom.

Both boilers stay on in summer as they do not use any gas unless heating water.

Heat users

The house is heated by hydronic coils in five zones in three concrete slabs at descending levels in the house, plus a fan-assisted radiator in the living room. Two manifolds are fed from a mixing valve, and water circulated by five, 240v Grunfos thermostatically-controlled 3-speed pumps.

We have only activated the outer coil on the lower slab coils. We are very fortunate that it flows via the master toilet and bathroom, laundry, kitchen, two guest bedrooms and to the living room on the lowest slab.
Hot tap water runs throughout the house with all piping insulated with 25mm thick foam tubing. External piping is further encased in 90mm stormwater piping.

Water delivery controls

Hydronic water is blended by the original tempering valve supplying two hydronic manifolds. Tap water is held to 50°C by a Reliance Heatguard Ultra tempering valve. This setting can be altered.

The three room thermostats in the home are very clever Honeywell model CM 907. They can be programmed in time blocks for every day of the week, can be over-ridden for one time block, set to a fixed temperature and adjusted for daylight savings. The lower slab thermostat in the living area also masters the upper slab in the entertainment area. The second thermostat in the upper level study controls the mid slab. The third thermostat in the master bathroom controls water to the towel rail.

OperationSolar control

The electronic differential controller, made by Whitnic Services of NSW, gets its data from 10volt thermistors, one at the array output and one at the storage tank top. It has three modes and a red light indicates the pump is on, which I positioned to see from the back door.

Gas supply

Gas was originally supplied by a bank of 40kg cylinders. These were replaced by a 190kg truck-filled tank, with pressure reducers at two boilers, and a circuit supplying the guest kitchen and fast-response gas heater in the living room.

Owner adjustments and monitoring

I wanted to monitor input and tank temperatures, so I bought three $10 electronic indoor/outdoor thermometers with remote sensors and mounted them next to the differential controller. I can feel the input arriving from the solar array, with one attached to the lowest hot connection on the storage tank, indicating roughly how much hot water is in the tank, and the other reads water delivery to the taps. These have max/min displays as well, useful for checking array performance or pump adjustments. An old clock-type dial indicator measures the temperature of water returning from the hydronic system, a rough indication of how much heat is in the slabs.
The electronic gauges are particularly useful to know how much heated water is available for a big load such as a spa fill or running the lounge room radiator. Monitoring incoming temperatures from the array allows me to tune up the flow rate for best performance just below steam occurring, and tells me if we have any problems when it’s pumping. An improvement would be digital readings from the differential controller’s thermistors.
We can adjust slab heating times in two zones and towel rail temperature, and boost heat in the lounge room by activating the fan-assisted radiator. We can control the temperature of the water leaving the fire water jacket. We cannot alter the temperature trigger points for the solar array. It might be useful to keep it pumping above 80°C to stop a steam blockage occurring.

When there’s a run of low solar-energy days we run the wood fire hotter. When there’s sunny days predicted, we can use less wood, or not light it.

As autumn starts, we open the hydronic valves and drive the wood heater hard to put as much heat as possible into selected slabs prior to cold snaps and overcast winter days. On a run of overcast days we open the damper on the wood heater.

Fine tuning and problems

We run the collector pump at the lowest of three speeds and fine-tuned the flow to 1.5l/min on the advice of the plumber. We’ve learnt that in summer we need to double the flow rate to avoid excessive pressure build-up.
The original thermistor on the solar array burnt out after one year and the surrounding insulation was charred! The new importer tells me the replacement thermistor is a tougher type.

Anything that stops the circulating pump while there’s sun on the vacuum tubes can create a blockage in the circuit that the circulating pump cannot overcome. When the thermistor on the roof fried, and when we lose power when the sun’s on the tubes, pressure builds up and the closed loop finally drops below it’s 0.2 bar pre-set pressure. This stops circulation for that day and we lose a little water as steam. When the pump is alive again it fails to get water circulating if the array is in sun. So if the system pressure gauge is zero, I know circulation has stopped and must be topped up. To fix it we fit the garden hose onto the fill point just below the pump, and run cold water until there are no bubbles passing the sight gauge. Our plumber has suggested an automatic supply for this.

Maintenance

Particle filters in the inlets to the tap boiler and both tempering/mixing valves need to be cleaned annually, the latter by removing the fitting gland, which is not a good design.

The Zilmet pressure storage tank needs its quiescent air pressure checked annually, and the whole tank replaced every five years. Pressure cylinders on my Citroen last indefinitely, with re-gassing, so we’ll see. The system needs to be de-pressured for accurate pressure checks.

The solar collector array needs to be hosed periodically to remove leaves.

Costs

Our gas costs about $730 for 550 litres per year, but my urban mate pays a fraction of our price! We really only use significant gas when we have guests, then it goes through the litres when the large boiler is doing a lot of the home heating. We average about 66 mjoules of gas per day in winter, and as little as 19 at other times. The Elgas truck doesn’t come from October to late April. In 2010 we used half the gas of 2009, mainly due to better windows and remembering to keep bedroom doors closed. We will get further significant reductions when our window conversions and internal glass partition are finished.

Total changeover cost, including towel rail and some bathroom alterations, was about $11,500 against an estimated $17,000. The local shire gave us a rebate of $250 and we received another $6900 in rebates. If hydronic slab heating was built into a new home, it may not be any more than other hot water and heating systems. Our 44 RECs were not sold because the supplier did not have an approved system with the tank size we used, so we missed out on around $1500. That’s a little plus for the environment as energy companies had to find an extra 44 RECs somewhere else.

Changed family habits

The dog is often asleep on the hottest sections of the hydronic loop, always in doorways or on the top of stairs. The cats love the laundry benches in winter.

To minimise the generation of greenhouse gas and gas bills we use most of our hot water first thing in the morning, giving the solar array the first opportunity to recover hot water lost. We built a wooden, pull-down rack below the laundry ceiling which now dries much of our cold weather washing.

We need to shut off the hydronic valve when spring is well-entrenched and must remember to open it when the first cool weather is predicted after Easter.

What next?

We are part-way through replacing most open-plan area windows with double glazing, with low U and SHGC value glass and argon gas in the space.

At the moment glaziers are installing a glass, openable air barrier at the top of the living area. This will zone the home into separate living and entertaining zones, reducing wood demands and cold air currents up the kitchen.
Stopping heat escaping is next. After a government-funded home assessment, this air entrapment work was to be financed by the now defunct Green Loans scheme. Another task is resealing all doors, and chasing air leaks along the brick-ceiling interfaces throughout the living spaces and external walls. This is to stop bushfire embers and smoke ingress; the home is to be a refuge as we’ve spent a lot of money on a 10-hour fire sprinkler system for all buildings.

I’m also planning to have the roof re-pointed; it’s amazing how much heat escapes from the fabric of the cathedral ceiling when you remove a capping tile on a cold day.

Much of the living room slab could be heated, in cooler weather, by direct sunlight, and possible when we replace dark green fibreglass on the pergola outside with clear sheets and retractable shade cloth.

I’d like an automatic system to over-ride the pump control in the main gas boiler, so the rail can be heated when the slab hydronics are off. This will probably involve some extra 240v relays to override the pump’s under-temperature and gas supply controls, which stop the pump when the hydronics are not on.

Due to firebox corrosion we will soon replace the wood heater. The next one will have a wet-back for more hydronic capability.

Suppliers

Green-accredited plumbers—Baw Baw Plumbing, Buln Buln East

Solar equipment suppliers—Phazer, Warragul

Glaziers—Walkies’s windows and glazing, and Warragul glass and glazing

Flue heat exchanger, gas room heater—Cosy heaters, Warragul

Monitoring thermometers—Dahlsens, Warragul

Fire protection system—The Farm Depot, Warragul

Gas heater installation—West Gippsland gas services, Warragul

Solar hot water for small spaces

Most evacuated tube solar hot water collectors use tubes at least 1700mm long. For installations where there isn’t much roof vertical space or where the panel needs to thermosyphon to a tank mounted low in the roof cavity, standard tubes are too long.

The Solarvox SVM30-58/850 and SVM35-58/850 systems consists of 30 or 35 evacuated tubes respectively. Each tube measures 58mm diameter and is just 850mm long. This results in a collector that is short but wide, making for a more flexible range of installation options.

The Solarvox systems can be mounted on balconies and even above windows, taking the place of eaves or awnings, so the collector can double as both hot water system and sunshade.

The collectors are suitable for thermosyphon as well as pumped systems and a complete 30 tube collector weighs 55kg. The tubes have passed a 25mm hail test and the collectors are designed to continue to collect heat even when missing some tubes.

RRP: $1080 for the 30 tube collector, $1280 for the 35 tube. Delivery is available, but pickup from Fairfield, VIC, is recommended.

Also in the latest issue of ReNew

Super-efficient hot water know how

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Richard Keech explains how he combined an evacuated tube solar collector and a heat pump to make a high efficiency hybrid water heater.

On my three-bedroom Melbourne house I have what might be the most efficient solar hot water system around. In the year since installation it has performed extremely well, and I’ve learnt a lot along the way. This article will consider aspects of solar hot water design and rationale that led me to the system I have now. Then it will look at the system as built and the lessons after one year of operation. My design for the system brings together some ideas about what makes for a more sustainable hot water system. Some of these ideas challenge conventional wisdom on the subject.

Crank it up
For hot water, the Your Home Technical Manual for example suggests to tilt the (north-facing) solar panels at an angle corresponding to the latitude of the location and “in some cases, it may be desirable to increase the angle somewhat to improve winter performance and reduce overheating in summer”. Despite this, it’s uncommon in my experience to see solar collectors tilted above 35°.

My interpretation of the situation is that it’s more than merely “desirable in some cases”—it’s really important to increase the tilt of solar collectors for hot water, but not PV. To appreciate why, we need to recognise the key difference between solar hot water and solar PV, namely, that solar hot water systems cannot make use of their surplus energy. Indeed excess summertime solar gain can be a problem as discussed in ReNew 113 (DIY Solar Hot Water Cover page 72). On the other hand, urban PV systems have the benefit that excess generation is simply exported to the grid.

Grid-connected PV systems are best configured for maximum annual solar gain. However, we need to apply a different rule of thumb for hot water—to configure for the maximum number of days with sufficient solar gain. This means cranking up the solar collectors to a much steeper angle. This is done to maximise solar gain in winter and to help reduce overheating problems in summer. To optimise for winter noon, the angle should be latitude plus 23.5°, which in Melbourne is 61°. Given that the angle of the sun is lower than its noon angle for most of the daylight hours, it follows that the collector angle should be even a little higher than this. I chose to tilt my collector at 64° from the horizontal.